Transit of Venus 2012 (WH)

Experiencing a transit is a unique astronomical observing event, but some are not as rare as a transit of Venus. More common transits that can be observed in the solar system are transits of Mercury (or an eclipse, as the moon transits the Sun). Transits of Venus come in pairs with the first transit separated by 122 years from the next pair. The second transit in the pair comes 8 years after the first (i.e. 2004 and 2012). The transit time from 1st contact to 4th contact of the disk of Venus on the face of the Sun in 2012 was about 6 hours and 45 minutes.

Our observing party on June 5, 2012 consisted of Joe Wilcox (Hawaii Space Grant Consortium Associate Director for Hawaii Community College), together with visiting observational experts: Bob McGown of Portland, Oregon; and Walter de Sagher of Belgium. Our plan was to join a number of mostly professional observers on the summit ridge of Mauna Kea for, at least, the first part of the transit event. We knew that the rangers planned to close the summit road and encourage the expected large crowds to congregate at Onizuka Visitor Center (elevation 9200 feet). Although college personnel were likely to be granted a pass at the roadblock, we chose to leave early from Kailua-Kona to avoid the expected traffic congestion. Leaving at 4 am, we drove the mostly empty winding road to the summit, arriving just after sunrise. The sky was clear, although the temperature was near freezing; and we had to stage our planned activities in the lee of a telescope dome to avoid a strong wind. With several hours of waiting before the mid-day start of the transit, we explored the area on foot. Joe and Walter are mountain climbers and made the short hike to the actual summit of Mauna Kea several times for altitude training. Bob used the opportunity to inspect what may become the site of a future thirty meter telescope (TMT).

As the transit time approached, we set up two Schmidt Newtonians, with two Nikon cameras with 300mm lenses using split diffraction filters and photographic Milar filters. We also deployed a Coronado H-alpha solar telescope. In addition we set up a Sunspotter to help several tourists enjoy the event. We watched carefully during the first and second contact of the disk of Venus. Other than our eye moving in and out of the focal plane of the 20mm eyepiece, we could not see a tear drop effect, a phenomenon that historically complicated accurate timing of transits and compromised efforts to calculate the Astronomical Unit. As the transit progressed, observers on the observatory ridge struggled with strong winds and the cold temperature. We decided to descend down to the Visitor Center and continue our observations there. When we arrived at the Onizuki Visitor Center, we were surprised by the large number of observers there, and the great variety of solar telescopes, including Cassagrains, Dobsons, refractors, and Sunspotters. There were about three people for each solar telescope. We counted seventy six solar telescopes in use.

Prof Joe did a mental calculation that the third and fourth contacts would not be visible from the Visitor Center, as the Sun would dip below a ridge. After briefly photographing through several deployed telescopes, and visiting with rangers and colleagues, we decided to continue our observing adventure at the Mauna Loa Atmospheric Observatory (elevation about 11,000 feet) across the saddle divide. Joe is acquainted with the NOAA Station Chief, John Barnes, as John had mentored two Hawaii Community College Space Grant Trainees during spring semester. Thus, we were welcome to enter the gated facility. After a brief tour of the small solar observatory, we ended up at the major Mauna Loa transit activity. Scientists from the Exploratorium in San Francisco were producing a broadcast of the transit and down-linking it to the world-wide web. Their control room had various monitors, including calcium, white, and H-alpha light. We could clearly see several flares on the solar limb in H-alpha light. Bob had the most observing experience and pointed out several other details that might have otherwise gone unnoticed. We found the event production very interesting, but still occasionally stepped outside to a small solar telescope to witness the transit “in person”. Again, no teardrop effect was observed at third contact and Venus’ fourth contact with the higher solar atmosphere of H-alpha light signaled the conclusion of our transit experience.

After the excitement of the transit had calmed, we visited with the Exploratorium scientist, and John Barnes facilitated a tour of several on-site research installations, including the hexapod array of thirteen microwave interferometer dishes for studying galaxies recessing through the cosmic background radiation. John also actuated the Lidar laser system for measuring atmospheric particulates (similar to, but less nimble than, the smaller portable Clidar system that had been used by the Hawaii Community College Space Grant Trainee students to profile Kona vog). A late drive back to Kailua-Kona ended a very successful observing day.

Photos by: Robert D. McGown FRAS

This was taken near the beginning of the transit and shows solar telescopes on the observatory ridge near the summit of Mauna Kea. Part of the UH 1-meter telescope is visible.

This was taken near the end of the transit in the Mauna Loa control room for the world-wide web broadcast. The monitors show the silhouette of Venus in calcium (blue), visible (yellowish), and H-alpha (red) light. Careful inspection indicates that 3rd contact will occur first in calcium, next in visible, and last in H-alpha; verifying relative levels of the solar atmosphere.

This was taken near the end of the transit in the Mauna Loa control room for the world-wide web broadcast. The monitors show the silhouette of Venus in calcium (blue), visible (yellowish), and H-alpha (red) light. Careful inspection indicates that 3rd contact will occur first in calcium, next in visible, and last in H-alpha; verifying relative levels of the solar atmosphere.